Search

Introduction: Visceral leishmaniasis (VL) is an important tropical and neglected disease and represents a serious global health problem. The initial interaction between the phagocytes and the parasite is crucial to determine the pathogen's capacity to initiate infection and it shapes the subsequent immune response that will develop. While type-1 T-cells induce IL-6, IL-1β, TNF-α, and IL-12 production by monocytes/macrophages to fight the infection, type-2 T-cells are associated with a regulatory phenotype (IL-10 and TGF-β) and successful infection establishment. Recently, our group demonstrated the role of an important Th1/Th17 T-cell population, the mucosal-associated invariant T (MAIT) cells, in VL. MAIT cells can respond to L. infantum by producing TNF-α and IFN-γ upon MR1-dependent activation., Objective and Methods: Here, we describe the impact of the MR1-blockage on L. infantum internalization on the functional profile of circulating neutrophils and monocytes as well as the impact of the MR1-blockage on the soluble mediator signatures of in vitro whole blood cultures., Results: Overall, our data showed that VL patients presents higher percentage of activated neutrophils than asymptomatic and non-infected controls. In addition, MR1 blockade led to lower TNF-α and TGF-β production by non-activated neutrophils from asymptomatic individuals. Moreover, TNF-α and IL-10 production by monocytes was higher in VL patients. In the analysis of soluble mediators produced in vitro , MR1-blockade induced a decrease of IFN-γ and an increase of IL-10, IL-27 and IL-33 in the cell cultures of AS group, a cytokine pattern associated with type 2 deleterious response., Discussion and Conclusion: These data corroborate the hypothesis that MR1-restricted responses are associated to a protective role during Leishmania infection., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision, (Copyright © 2024 Borges-Fernandes, de Lima Moreira, Pereira, Pascoal-Xavier, Lopes Ribeiro, Costa-Rocha, Lopes, Moreira, Araújo, Teixeira-Carvalho, Brito-de-Sousa, de Carvalho, Mourão, Campos, Borges, Carneiro, Tsuji, Martins-Filho, Coelho-dos-Reis and Peruhype-Magalhães.)

Mucosal-associated invariant T (MAIT) cells are restricted by MR1 and are known to protect against bacterial and viral infections. Our understanding of the role of MAIT cells in parasitic infections, such as visceral leishmaniasis (VL) caused by protozoan parasites of Leishmania donovani , is limited. This study showed that in response to L. infantum , human peripheral blood MAIT cells from children with leishmaniasis produced TNF and IFN-γ in an MR1-dependent manner. The overall frequency of MAIT cells was inversely correlated with alanine aminotransferase levels, a specific marker of liver damage strongly associated with severe hepatic involvement in VL. In addition, there was a positive correlation between total protein levels and the frequency of IL-17A + CD8 + MAIT cells, whereby reduced total protein levels are a marker of liver and kidney damage. Furthermore, the frequencies of IFN-γ + and IL-10 + MAIT cells were inversely correlated with hemoglobin levels, a marker of severe anemia. In asymptomatic individuals and VL patients after treatment, MAIT cells also produced IL-17A, a cytokine signature associated with resistance to visceral leishmaniasis, suggesting that MAIT cells play important role in protecting against VL. In summary, these results broaden our understanding of MAIT-cell immunity to include protection against parasitic infections, with implications for MAIT-cell-based therapeutics and vaccines. At last, this study paves the way for the investigation of putative MAIT cell antigens that could exist in the context of Leishmania infection., Competing Interests: JM, ZC, and SE are inventor of patents describing MR1 antigens and MR1 tetramers. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Moreira, Borges-Fernandes, Pascoal-Xavier, Ribeiro, Pereira, Pediongco, Araújo, Teixeira-Carvalho, de Carvalho, Mourão, Campos, Borges, Carneiro, Chen, Saunders, McConville, Tsuji, McCluskey, Martins-Filho, Eckle, Coelho-dos-Reis and Peruhype-Magalhães.)